It is typically the case that an optical signal transported over an optical transport, such as an optical fiber, must be coupled between that optical fiber and another optical fiber or an optoelectronic device. Typically, the end face of the optical fiber is outfitted with an optical connector of a given, standardized form factor, e.g., MT, which connector can be coupled to a mating optical connector on the other fiber or optoelectronic device.
Optical cables that are connected to each other through a pair of mating connectors may comprise a single optical fiber. However, more and more commonly, optical cables contain a plurality of optical fibers and the light in each optical fiber in the cable is coupled through a pair of mating connectors to a corresponding optical fiber in another cable or a corresponding optical receiver or transmitter in an optoelectronic component.
Optical connectors generally must be fabricated extremely precisely to ensure that as much light as possible is transmitted through the interfacing fibers so as to minimize signal loss during transmission. In a typical optical fiber, the light is generally contained only within the core of the fiber, which typically may be about 10 microns in diameter for a single-mode fiber or about 50 microns in diameter for a multi-mode fiber. A speck of dust typically is greater than 10 microns in cross section. Accordingly, a single speck of dust at the interface of two fibers can substantially or fully block the optical signal in a fiber from getting through the connectors.
Accordingly, it is well known to use expanded beam connectors, especially in situations where it is likely that connections will be made in the field, and particularly in rugged or dusty environments. Expanded beam connectors include optics (e.g., lenses) of the connector (i.e., the end of the connector that is designed to be connected to another optical connector or optoelectronic device). Depending, of course, on the direction of light travel through the connector, the lens either expands a beam exiting a fiber to a greater cross section for coupling to the corresponding lens of a mating connector or images a beam entering the lens from a corresponding lens of another connector to an image point in the face of a fiber. Generally, such interfaces employ collimating optics so that the light beams between the optics of the two mating connectors are collimated and of a spot size much larger than the core of the fiber from which it emanated (and the core of the fiber into which it is being directed).